Fish shrink as oceans warm

Fish of all species look set to shrink in size by up to a fifth as the oceans continue to warm.

Warmer seas mean less-oxygenated water, which could have a significant effect on the size of fish, the University of British Columbia researchers say.

The team used computer modeling to study more than 600 species of fish from oceans around the world. And, they found, the fish's maximum body weight could fall by between 14 and 20 percent between the years 2000 and 2050, with the tropics most seriously affected.

"We were surprised to see such a large decrease in fish size," says William Cheung, an assistant professor at the UBC Fisheries Centre.

"Marine fish are generally known to respond to climate change through changing distribution and seasonality. But the unexpectedly big effect that climate change could have on body size suggests that we may be missing a big piece of the puzzle of understanding climate change effects in the ocean."

As fish grow, they need to be able to extract more oxygen from the water around them, says Daniel Pauly, principal investigator with UBC’s Sea Around Us Project.

"It’s a constant challenge for fish to get enough oxygen from water to grow, and the situation gets worse as fish get bigger," he says.

"A warmer and less-oxygenated ocean, as predicted under climate change, would make it more difficult for bigger fish to get enough oxygen, which means they will stop growing sooner."